Formation process of ultrathin multilayer films of molybdenum oxide by alternate adsorption of octamolybdate and linear polycations

Multilayer films of molybdenum oxide were prepared by means of alternate adsorption of ammonium octamolybdate ((NH₄)₄[Mo₈O₂₆]) and poly(allylamine hydrochloride) (PAH). The films were reproducibly grown at each adsorption cycle, as monitored by a quartz crystal microbalance. Adsorption of PAH on the surface of a molybdenum oxide layer was saturated with a constant thickness of 32 ± 21 Å. On the other hand, adsorption of octamolybdate on the PAH layer did not show saturation. The thickness of the oxide layer in the individual adsorption step increased with the adsorption time at a rate of ca. 5.7 Å/min due to condensation of the adsorbed octamolybdate and the resulting loss of negative charges. The surface of the resulted films was relatively flat with height difference of less than 10 nm, and the film thickness was constant over a large area, as confirmed by scanning electron microscopy.